1. Field of the Invention
The subject invention relates to a light emitting assembly of the type including light emitting diodes (L.E.D.), and more particularly, light assemblies for mounting to a planar support.
2. Description of the Prior Art
Light emitting diode (L.E.D.) light assemblies use less electrical power and thus are becoming more common as L.E.D. technology continues to improve. An important factor driving this acceptance of L.E.D.s is the increasingly attractive life cycle cost of such L.E.D. light assemblies. The expected useful life of properly designed L.E.D. light assemblies can exceed 10-12 years, or 70,000 hours, compared to a nominal 2-3 year life of high-intensity discharge (H.I.D.) lamps. An example of a properly designed L.E.D. light assembly is disclosed in U.S. Pat. No. 5,857,767 to the present inventor, Peter A. Hochstein. At least a fifty percent (50%) energy savings is possible when H.I.D. light assemblies are replaced with such properly designed L.E.D. light assemblies. The energy related cost savings allow the L.E.D. light assemblies to pay for themselves in a relatively short period of time.
Recently, municipalities desire to replace their wall-mounted H.I.D. light assemblies, such as the low bay light assemblies used in parking garages, with L.E.D. light assemblies. Many existing L.E.D. light assemblies perform well under ideal operating conditions, or prior to being mounted to a planar surface or wall, but due to poor thermal management, the L.E.D. light assemblies do not perform well when mounted on a planar surface. The existing wall-mounted light assemblies typically include heat sinks enclosed in a poorly ventilated housing. Convective cooling of the light assembly is limited due to the planar wall and geometry of the housing.
Many existing low bay light assemblies include fins extending vertically from the heat sink to improve thermal management, such as the L.E.D. light assembly disclosed in the Pacific Northwest National Laboratory Report: Demonstration Assessment of Light-Emitting Diode (LED) Area Lights for a Commercial Garage, dated November 2008 (see page 2.4). However, when such L.E.D. light assemblies are mounted to a planar surface, the fins are disposed adjacent the planar surface or housing, and thus cannot effectively shed heat to ambient air. In such cases, a 10° C. per Watt thermal resistance is typical. The aggregate sum of all thermal resistances of the L.E.D. light assembly is then approximately 22° C. per Watt, and the junction temperature rise of a 3 Watt L.E.D. would be approximately 66° C. At ordinary ambient temperatures in the 20° C. ranges, the L.E.D. junction would be operating at about 86° C., which reduces the useful life of the L.E.D. light assembly from 70,000 hours to approximately 20,000 hours of useful life.